1. Field of the Invention
The present invention relates to a mobile communication terminal for conducting radio communication over a mobile communication network or mobile satellite communication network.
2. Description of the Background Art
Conventionally, in the mobile communication the mobile communication terminal conducts radio communication with a base station, and in the mobile satellite communication it communicates with the base station via a satellite. In the radio communication there are set various modes of communication corresponding to the contents of communication, such as a standby mode in which to stand by for a communication, a channel switching communication mode and a packet communication mode.
FIG. 6 shows various modes of communication that are used in the mobile communication terminal. These modes require high-speed signal processing which involves complex operations on various digital signals; such processing is usually carried out using a DSP (Digital Signal Processor).
FIG. 7 depicts DSP clock frequencies necessary for operating the DSP in the mobile communication terminal in various modes of communication services. Since the modes of communication are different in the amounts of data and the contents of operations that the DSP processes, the DSP clock frequencies that are needed in the individual modes take different values. As indicated by the value "a" in FIG. 7, the required value of the DSP clock frequency in the standby mode is usually lower than in any other modes. In FIG. 7, the required values "b" and "c" of the DSP clock frequency in a high speed data communication mode and a voice communication mode are shown together with the standby mode, such that the clock value increases in the order of "a"-"b"-"c" for convenience of explanation. And, in the conventional mobile communication terminal the DSP clock frequency is fixed at the maximum clock frequency value "c" that covers all modes of communication services.
Since the conventional mobile communication terminal uses the DSP clock fixed at the maximum clock frequency that covers all the modes of communication services as mentioned above, the DSP power consumption is constant irrespective of the modes of communication services and is heavy. On the other hand, the necessary DSP clock frequency in each communication mode, for example, in the standby mode, may be the minimum value "a" as depicted in FIG. 7, and in the high speed data communication mode and in the voice communication mode, the clock frequency needs only to be set partly high (the values "b" and "c"). Since the power consumption in the DSP fluctuates with the clock frequency value, the power which is included in the DSP power consumption and corresponds to the shaded area in FIG. 7, goes to waste. Accordingly, taking account of the fact that the time of the standby mode is very longer than the times of the other communication modes, the rate of power wasted by the DSP, that is, the rate of wastage of the DSP power consumption is appreciably great as follows: EQU (Rate of wastage of DSP power consumption)=(1-a/c).times.100(%)
The present invention is intended to provide a mobile communication terminal for radio communications in various communication modes, which may reduce the DSP power consumption.